The present invention relates to detersive enzyme composite particles having a an acidic barrier layer and a physical barrier layer. More particularly, the present invention relates to an enzyme particle, such as a prill, having an enzyme containing core which is coated with an acidic barrier layer and a physical barrier coating on the acidic barrier layer for the protection of the enzyme.
The incorporation of detersive enzymes into dishwashing detergents is well known in the arena of both automatic dishwashing (ADW) formulas, and liquid hand dishwashing formulas (LDLs). A recognized need in ADWs compositions is to have present one or more ingredients which improve the removal of tough foods and stains (e.g., tea, coffee, cocoa, etc.) from consumer articles. Strong alkalis like sodium hydroxide, bleaches such as hypochlorite, builders such as phosphates and the like can help in varying degrees. Moreover, improved ADWs make use of a source of hydrogen peroxide, optionally with a bleach activator such as TAED, as noted. In addition, enzymes such as commercial proteolytic and amylolytic enzymes can be used. The alpha-amylase component provides at least some benefit with respect to the starchy soil removal properties of the ADW. ADWs containing amylases typically can also deliver a somewhat more moderate wash pH in use, and can remove starchy soils while avoiding delivering large weight equivalents of sodium hydroxide on a per-gram-of-product basis.
Typically, the enzyme component of a liquid ADW composition is added to the ADW composition in liquid form. While this allows the liquid ADW composition to have the benefits of enzyme content discussed above, there are also disadvantages, most notably that the liquid ADW composition must be formulated at pH levels that are lower than those conventionally used, because enzymes are rendered ineffectual after being exposed to high pH environments. Because formulating at lower pH levels can harm cleaning performance (high pH enhances cleaning by aiding the rates of hydration and hydrolysis), a need exists for an enzyme material that is stable in a high pH environment.
One approach to improving enzyme stability in a high pH (greater than 9) ADW detergent composition is to add the enzyme as a solid particle. This xe2x80x9cenzyme particlexe2x80x9d consists of a solid core enzyme material coated with a barrier layer material. For example, a solid enzyme material can be coated with a thick wax layer material to form an enzyme particle and then this enzyme particle may be added to the ADW composition.
But the use of these wax coatings have several disadvantages. Most notably, when the waxes melt and are released into the wash solution, due to the high temperature encountered during the automatic dishwashing process, they tend to cause undesirable filming on glass, stainless steel and plastic surfaces. This filming is a particular problem with ADW formulas, which often contain no significant surfactants in the composition. Additionally, thick wax coatings can also reduce the rate of dissolution of the enzyme-containing particle, which may reduce the cleaning contribution of the enzyme, by reducing the time it is resident in the wash solution.
Given the foregoing there is a continuing need to develop new compositions for the enzyme particles that will protect the enzyme core material when the particle is added to a high pH liquid ADW composition, and yet at the same time, not produce the undesirable filming associated with wax coatings, nor inhibit the rapid dissolution of the enzyme-containing particles.
Accordingly, it is a benefit of the present invention that an enzyme particle with a two-layer coating effectively protects the core enzyme material from high pH liquid compositions, without the deleterious effects of the thick wax layer coating noted above. This two-layer consists of an interior chemical barrier, preferably an acidic barrier, which is itself coated with an exterior physical barrier. The physical barrier prevents the chemical barrier from reacting directly with the alkaline liquid product (particularly important when the chemical barrier is an acidic barrier), while the chemical barrier effectively neutralizes any stray hydroxyl groups of the alkaline product that permeate past the physical barrier coating. The chemical and physical barrier thus work together and provide complementary functions. Preferred physical barriers include polymeric coatings that are insoluble in the liquid automatic dishwashing detergent composition but soluble, meltable or dispersable under the pH, temperature and agitation conditions of an ADW device.
In addition to their use in ADW compositions, these improved enzyme particles may be incorporated into light-duty liquid (LDL) detergent compositions useful for manual dishwashing as well. Enzymes, typically commercial proteolytic and amylolytic enzymes, provide LDL compositions with a variety of benefits, including improved cleaning performance as well as preferred skin mildness and xe2x80x9cskin feelxe2x80x9d aesthetics (i.e. the product does not feel slimy or slippery in the hands of a consumer). By adding enzymes to a LDL composition in the form of an enzyme particle, stability of enzymes in a LDL composition can be enhanced. Release of the enzymes is accomplished easily as a result of the agitation and increased temperature during manual dishwashing by the consumer.
U.S. Pat. No. 4,965,012 discloses an encapsulating enzyme composition.
U.S. Pat. Nos. 4,381,247; 4,707,287; 4,965,012; 4,973,417; 5,093,021 and 5,254,287 all disclose enzyme particles for granular detergent compositions. U.S. Pat. Nos. 4,526,698; 5,078,895; 5,332,518; 5,340,496; 5,366,655; 5,462,804 and WO/95/02670 all disclose coated bleach particles.
U.S. Pat. No. 5,200,236 discloses a method for wax encapsulating particles.
U.S. Pat. No. 3,908,045 discloses coating a solid bleach particle with a first layer of fatty acid and a second layer of base (alkali hydroxide) treated fatty acid.
The invention meets the needs above by providing a detersive enzyme composite particle suitable for incorporation in a liquid detergent composition, including, an enzyme containing core material, an acidic barrier layer coated on the enzyme containing core material, and a physical barrier layer coated on the acidic barrier layer.